Selective attention. A type of attention which involves focusing on a specific aspect of a scene while ignoring other aspects. Selective attention can be conscious (as when one chooses to attend to an interesting object, like a tv, instead of a less interesting one, like a coffee table) or unconscious (as in a scene of a green field with a single red tulip - the tulip will receive attention initially). Often, we think we have taken in an entire scene when, in reality, we have processed only the area we are attending to and only have a general "gist" of the rest of the scene (see links for examples, where you can watch this happen to you).

examples:

Focusing on one voice during a party in which many people are speaking

Various theories have been proposed about how certain aspects of a scene receive attention while others do not. Anne Treisman's Feature integration theory is widely accepted.
Kyle Cave's FeatureGate model builds on Treisman's ideas, and proposes two mechanisms of visual selection, bottom-up and top-down, which roughly correlate with unconscious and conscious attentional selection, respectively.